It depends on what basis the council collected your data and what you agreed they could do with it.

You are required to give your tenants your name and an address where legal notices can be served on you and rent paid. If you haven't done that, it's possible for the tenant to decline to pay rent until you do (they have to catch up - there's no free period). So it's not that the council have given the tenant anything they shouldn't already have.

I dont know the definitive answer for HMO`s as mine are all single lets so you may well be right . My C/O address is accepted by the council . But the address for the HMO also has to be displayed on the premises as well as I understand it .

All visitors could see that as well so a personal address could leave the owner a bit vulnerable . I would imagine a bona fide office address would suffice or a suitably registered letting agent solicitors or accountants so you can be contacted / served notices etc if needs be .

The telephone number maybe linked though to whoever can deal with a management emergency but not necessarily the address

For a HMO you have to inform the tenants of your name and address.. Your name and address is on record with the council and in many cases online in the form of results of freedom of information requests. For example im quite within my rights to ask a council for a list of all HMO owners and Addreses in their area. Many people have done this and put up online.

All opinions are my own and do not reflect those of my firm. No comment made should be taken as legal advice and you should consult a solicitor or other legal professional for advice on your specific situation.